Apparatus for microwave heating of dielectric materials



April 12,1949. KINN 2,466,853

APPARATUS FOR MICROWAVE HEATING 0F DIELECTRIC MATERIALS Filed 901.. 4,1946 WITNESSES: I INVENTOR AYM ZZeaa/ore P/r/m.

Patented Apr. 12, 1949 APPARATUS FOR MICROWAVE HEATING OF DIELECTRICMATERIALS Theodore I. Kinn, Baltimore, Md., assignor to WestinghouseElectric Corporation, East Pittsburgh, -Pa., a corporation ofPennsylvania Application October 4, 1946, Serial No. 701,306

'10 Claims. 1

'lhis invention relates to microwave heating, and has particularrelation to apparatus for heating dielectric material with electricenergy at frequencies in the microwave region. In heating dielectricmaterial with conventional high-frequency apparatus, difficulty isencountered in providing a sufficiently fast heating rate. It has beensuggested that heating might be accomplished at a very rapid rate with.the use of electric energy at microwave frequencies. Difiiculty isencountered in such an arrangement in providing'a uniform field to giveuniform heating because of uneven field distribution in a hollow bodyresonator.

It is, accordingly, an object of my invention to provide'newand improvedapparatus for heating a dielectric material.

Another object of my invention is to provide novel apparatus for heatinga dielectric material with electric energy at microwave frequencies.

Still another object of my invention is to provide novel apparatus forheating a dielectric material uniformly and rapidly with electric energyat frequencies at the microwave region.

In accordance with my invention, the dielectric material is to be placedbetween a pair of electrodes which are coupled to a hollow bodyresonator, or wave guide, to receive energy therefrom. By thisarrangement, uniform and rapid heating may be accomplished.

The features of my invention which are believed to be novel are setforth with more particularity in the accompanying claims. The inventionitself, together with additonal objects and advantages thereof, may bebetter understood from the following description of a specificembodiment, when read in connection with the accompanying drawing, inwhich the single figure is a diagrammatic illustration of a preferredembodiment of my invention.

As shown in the drawing, a dielectric material I is positioned between apair of spaced electrodes 2 and 3, The electrodes 2 and 3 are coupled toa hollow body 4 adapted to have high-frequency electromagneticoscillations established therein. The hollow body 4 may be a suitablewave guide, or cavity resonator, into which energy is introduced fromany suitable high-frequency source.

The electrodes 2 and 3 form energy-trans ferring means to transferenergy from the hollow body 4 to the material I. The electrodes arecoupled to the guide at spacially and electrically spaced points,preferably by means of suitable coupling loops 5 and 6. The points ofcoupling are electrically spaced by n half-wave lengths of 2 theoscillations for which the body is designed, where n is a whole number,preferably by one half wave length. With such spacing, it is evidentthat the maximum difference is obtained between the two coupling points.Thus, with maximum current in the coupling loop 5 at any particularinstant, there is also a maximum current of opposite polarity at thecoupling loop 6.

The electrode 2 is connected to the coupling loop 5 by a conductive leadI, while electrode '3 is connected to coupling loop 6 by a conductivelead 8. These leads 1 and '8 are preferably an odd quarterwave lengthlong. Consequently, with a maximum current at the coupling loops 5 and6, maximum voltage difference appears between electrodes 2 and 3.

It is then apparent that an alternating voltage of high frequencyappears between electrodes 2 and 3. As a result, a high-frequencyelectric field is established between these electrodes for heating thematerial.

Although I have shown and described a preferred embodiment of myinvention, I am aware that many modifications thereof may be madewithout departing from the spirit of the invention. I do not intendtherefore to limit my invention to the specific embodiment disclosedsince I have also disclosed a manner of taking energy from a wave-guidein which the energy i introduced and is conducted, the energy beingwithdrawn through the coaction of two points spaced along thewave-guide.

I claim as my invention:

1. Apparatus for use in heating a dielectric material comprising, incombination, a hollow body adapted to have high-frequencyelectromagnetic oscillations established therein, a pair of spacedelectrodes externally of said hollow body and positioned to receive thematerial therebetween, coupling devices at a plurality of spacially andelectrically spaced points of said hollow body for taking electricalenergy from said hollow body, and conductor means from said couplingdevices to said electrodes for delivering said energy to saidelectrodes.

2. Apparatus as set forth in claim 1 wherein said points areelectrically spaced by a multiple of one half wave length of theoscillation for which the body is designed.

3. Apparatus as set forth in claim 1 wherein said conductor meanscomprises a separate conductive lead for each electrode having a lengthapproximately equal to an odd number of quarter wave lengths of theoscillation for which said hollow body is designed.

4. Apparatus for heating a dielectric material comprising, incombination, a hollow envelope comprising a wave-guide adapted to havehighfrequency electromagnetic oscillatory wave energy introduced thereinand to conduct such energy therealong, a pair of spaced electrodesexternally of said envelope and positioned to receive the materialtherebetween for heat-treatment, means electrically coupling saidelectrodes to said waveguide, comprising coupling devices at spaciallyand electrically spaced points of said wave-guide, adapted to be excitedby said energy, and comprising conductors from said coupling devices tosaid spaced electrodes, whereby to establish a field between theelectrodes to heat the material.

5. Apparatus as set forth in claim 4, but characterized further by saidpoints being located along said wave-guide so as to be electricallyspaced by a multiple of one-half wave length of the oscillations of saidwave.

6. Apparatus as set forth in claim 5, but characterized further by saidcoupling devices comprising magnetic loop couplers, and said conductorshaving a length approximately equal to an odd number of quarter-wavelengths of the oscillation of said energy.

7. Apparatus for high-frequency heating of material, comprising, incombination, a hollow envelope comprising a wave-guide adapted to havehigh-frequency electromagnetic oscillatory wave energy establishedtherein, and to conduct such energy therealong, energy transferringmeans externally of said envelope for delivering electrical energy tosaid material, energy-absorbing coupling devices at spacially andelectrically spaced points of said wave-guide, for taking energy fromsaid wave-guide, conductor means extending from said coupling devices tosaid energy-transferring means for conducting the energy taken from thewave-guide by said coupling devices to said energy-transferring means.

8. Apparatus as set forth in claim 7, but characterized further by saidcoupling devices comprising magnetic loop couplers, and said conductormeans comprising conductors, each having a length approximately equal toan odd number of quarterwave lengths of the oscillations of said energy.

9. Apparatus as set forth in claim 7, but characterized further by saidpoints being located along said wave-guide so as to be electricallyspaced by a multiple of one-half wave length of the oscillations of saidwave.

10. Apparatus as set forth in claim 9, but characterized further by saidcoupling devices comprising magnetic loop couplers, and said conductormeans comprising conductors, each having a length approximately equal toan odd number of quarter-wave lengths of the oscillations of saidenergy.

THEODORE P. KINN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,239,069 Worden et al. Apr. 22,1941 2,245,669 Hollmann June 17, 1941 2,248,840 Wilkoff July 8, 19412,370,161 Hansen Feb. 27, 1945

